After the upgrade to WordPress 2.9 I tried to change some files - mainly language files with poEdit.
But after uploading them WordPress 2.9 doesn't run normally - eg. the tags menu in editor window doesn't work any more or the upload file menu in editor menu doesn't work.
My question now: Does WP 2.9 now test its installation? Is there an integrity test of all files? It's quite strange that such change could destroy some parts of functions.